1. Technical Field
The present invention relates to an electron beam apparatus for providing an evaluation of a sample, such as a semiconductor wafer, that has a pattern with a minimum line width not greater than 0.1 μm with a high throughput, and further to an electron beam apparatus for irradiating a sample (i.e., a target), such as a part of a semiconductor wafer, with an electron beam having a large current density.
The present invention also relates to an aberration correction optical apparatus for a charged particle beam optical system, and more specifically, to an aberration correction optical apparatus comprising a plurality of multi-polar Wien filters and operable to compensate for an aberration in an optical system using a charged particle beam, such as an electron beam, as well as to an image projection optical system and a scanning type optical system, both of which are incorporated with the same apparatus.
2. Background Art
In a conventional electron beam apparatus using an image projection optical system, irradiation of a sample has been provided with a beam from an electron gun having a flat cathode defined by a planar surface for an electron beam emission or a convex shaped cathode defined by a convex shaped surface for the electron beam emission. In addition, a conventional electron gun for generating an X-ray has been designed and manufactured by employing a Pierce type electron gun (i.e., a specific type of electron gun made with a triode configuration composed of a cathode, Wehnelt and an anode).
Technology for compensating for the aberration in the optical system employing the Wien filter used with the charged particle beam including the electron beam have been already presented, as disclosed in the following cited documents 1 to 4. Among those, the cited document 1 has disclosed a method in which the Wien filter is operated under bidirectional focusing and nondispersive condition by overlapping a dipole and a quadrupole types of orthogonally intersecting electric and magnetic fields, and in which brightness of the quadrupolar electric and magnetic fields may be controlled so as to induce a spherical aberration and an axial chromatic aberration of equivalent amounts but of an opposite sign to those generated by an optical system employed to thereby cancel those aberrations introduced by the employed optical system. According to this method, in order to prevent any second-order geometric aberrations from being newly introduced by a corrector, it is effective for both H-trajectory and G-trajectory to take a symmetric or an anti-symmetric trajectory relative to ½ plane of a corrector optical trajectory length and again to take an anti-symmetric or a symmetric trajectory relative to ¼, ¾ plane of the corrector optical trajectory length, and taking such a trajectory defining double symmetry can also inhibit any chroma of third-order or magnification scale chromatic aberration of first-order from being newly introduced.
On the other hand, the inventions as disclosed in the cited documents 2 to 4 are directed to a method, which allows for conditioning the chromatic aberration to appear in a round shape independently from directions and also conditioning a shape of the third-order aberration to appear in a circular shape, by overlapping a hexapole and an octopole types of orthogonally intersecting electric and magnetic fields, in addition to those from the dipole and the quadrupole types.